Shortly afterwards, Robert Oppenheimer recruited him from Chicago, where he was collaborating with Enrico Fermi and Edward Teller on the first nuclear reactors, to the Los Alamos National Laboratory.

Later he joined University of Chicago Metallurgical Laboratory and worked under Edward Teller's supervision, who encouraged him to move into theoretical physics.

At Los Alamos in the late 1940s and early 1950s a group of researchers led by Metropolis, including John von Neumann and Stanislaw Ulam, developed the Monte Carlo method.

Metropolis was deeply involved in the very first use of the Monte Carlo method, rewiring the ENIAC computer to perform simulations of a nuclear core in 1948.

[6] In 1953 Metropolis was credited as a co-author of a paper entitled Equation of State Calculations by Fast Computing Machines.

[7] This landmark paper showed the first numerical simulations of a liquid and introduced a new Monte Carlo computational method for doing so.

In recent years a controversy has arisen as to whether Metropolis actually made significant contributions to the Equation of State Calculations paper.

Metropolis was also awarded the Pioneer Medal by the Institute of Electrical and Electronics Engineers, and was a fellow of the American Physical Society.

[11] In his memoirs,[12] Stanislaw Ulam remembers that a small group, including himself, Metropolis, Calkin, Konopinski, Kistiakowsky, Teller and von Neumann, spent several evenings at Los Alamos playing poker.

They played for very small sums, but: "Metropolis once described what a triumph it was to win ten dollars from John von Neumann, author of a famous treatise on game theory.